Congratulations, you skipped the story
Did you read the text at the very end of the game?
Do you know what insanity is?
Turn off the last TV set
Take a trip with Pam
Unlock all combos
Smash all crystals
Kill everyone
Solve all puzzles
Kill 20 enemies in co-op mode
Die in co-op mode
Beat all bosses in co-op mode
Kill 50 frozen enemies
Chop down the tree
Arena completed.
The tree falls!